The present invention relates generally to cardiac medical devices. In some embodiments, the invention relates generally to cardiac medical devices used both for monitoring the state of a patient and delivering therapy to the patient.
Cardiac medical devices can include diagnostic monitoring equipment, external medical device systems, and implantable medical devices (IMDs). Examples of such IMDs can include implantable hemodynamic monitors (IHMs), implantable cardioverter-defibrillators (ICDs), cardiac pacemakers, cardiac resynchronization therapy (CRT) pacing devices, and drug delivery devices.
As is known, ICDs are configured with one or more sensors, with each sensor generally used to monitor a distinct cardiac parameter of the patient. Upon interpreting one or more of the cardiac parameters as arrhythmic in nature, the ICDs, in turn, can be used to deliver an appropriate therapy to the patient, with such therapies including pacing and/or defibrillation. Unfortunately, identifying the exact source of an arrhythmia can sometimes be a challenge to both ICDs and the physicians taking care of patients with such ICDs.
For example, ICDs can have difficulty distinguishing between ventricular tachyarrhythmias and supraventricular tachycardias. As is known, ventricular tachyarrhythmias originate in the ventricular region of the heart, while supraventricular tachycardias originate above the ventricular region of the heart, e.g., in the atrial region of the heart or the atrioventricular (AV) node. As should be appreciated, ventricular tachyarrhythmias are considered the more severe cardiac event of the two for the patient.
One reason for the above-described difficulty is that measured signal parameters, for example, an electrogram (EGM) or timing of EGM from different chambers of the heart, for each of these cardiac events can be similar, and in turn, interpreted similarly by the ICDs. Because of this, in cases when supraventricular tachycardias occur, the ICDs may deliver inappropriate therapy. Such inappropriate therapies constitute a significant source of physical and emotional distress for patients, and can lead to early depletion of the ICD battery.
One specific example of a situation in which it can be difficult for the device to distinguish between ventricular tachyarrhythmias supraventricular tachycardias occurs when discriminating between supraventricular tachycardias having 1:1 antegrade conduction and ventricular tachyarrhythmias having 1:1 retrograde conduction.
In an attempt to solve the problem, those skilled in the art have used various mathematical algorithms to more effectively utilize the quantitative aspects of the signal parameters measured by the devices (e.g., EGM morphology, timing relationships between 2 or more EGMs, etc). This approach has generally been found to have variable success. By implementing these algorithms (e.g., via controllers) within ICDs, the incidence of inappropriate therapy was reduced from that of the early generation ICDs and the later developed dual-chamber ICDs. However, the inappropriate therapy was still found to occur.
What is needed are medical devices and systematic methods used to prevent the incidence of inappropriate therapy, while also being adapted to limit other risks to the patient when using such devices and methods.